1,4-Butanediol is an organic compound that can be a raw material of butadiene which is important as a monomer of synthetic rubber, and is an important material, in particular, in the tire industry. In recent years, the technique for conversion from a production process of basic chemicals relying on petroleum to a production process from renewable resources such as plant resources has been developed and practical realization thereof is steadily progressing. Also regarding 1,4-butanediol, for example, a production technique from saccharides as a raw material by recombinant Escherichia coli is known (Patent Document 1).
The biosynthesis pathway of 1,4-butanediol is shown in FIG. 1. Specifically, 1,4-butanediol can be biosynthesized, for example, from succinate or α-ketoglutarate as a starting material.
In the pathway starting from succinate, succinate is converted into 1,4-butanediol via succinyl CoA, succinyl semialdehyde, 4-hydroxybutyrate, 4-hydroxybutyryl CoA, and 4-hydroxybutyraldehyde. Enzymes that catalyze these reactions are (a) succinyl-CoA synthase, (b) CoA-dependent succinate semialdehyde dehydrogenase, (e) 4-hydroxybutyrate dehydrogenase, (f) 4-hydroxybutyryl-CoA transferase, (g) 4-hydroxybutyryl-CoA reductase, and (h) alcohol dehydrogenase, respectively (FIG. 1). Every organism has (a) succinyl-CoA synthase.
Also, there is a pathway that directly converts succinate into succinyl semialdehyde. In that case, succinate is converted into 1,4-butanediol via succinyl semialdehyde, 4-hydroxybutyrate, 4-hydroxybutyryl CoA, and 4-hydroxybutyraldehyde. The enzyme that catalyzes the reaction of converting succinate into succinyl semialdehyde is (c) succinate semialdehyde dehydrogenase (FIG. 1).
On the other hand, in the pathway starting from α-ketoglutarate, α-ketoglutarate is converted into 1,4-butanediol via succinyl semialdehyde, 4-hydroxybutyrate, 4-hydroxybutyryl CoA, and 4-hydroxybutyraldehyde. The enzyme that catalyzes the reaction of converting α-ketoglutarate into succinyl semialdehyde is (d) 2-oxoglutarate decarboxylase (FIG. 1).
Further, there is a pathway that generates 4-hydroxybutyraldehyde directly from 4-hydroxybutyrate by (i) 4-hydroxybutyraldehyde dehydrogenase (FIG. 1).
Among C1 compounds, methanol is produced at a low cost from natural gas, synthetic gas which is a mixed gas of carbon monooxide, carbon dioxide and hydrogen obtained by incinerating waste such as biomass and municipal waste, and so on. Natural gas is focused as a next-generation energy source because it abundantly exists in fossil resources, and generates a relatively small amount of CO2, and transition from conventional petroleum to natural gas is progressing. Methanol is easy to handle and stock because of its water solubility and so on, and is also suited as a carbon source in microbial culture.
A methylotroph is a general name for a C1 compound assimilating microorganism that uses a carbon compound not having a C—C bond in the molecule, e.g., methane, methanol, methylamine, dimethylamine, trimethylamine or the like as a sole carbon source or energy source. Any microorganisms called methanotroph, methane-oxidizing bacteria, methanol assimilating bacteria, methanol assimilating yeast, methanol assimilating microorganism belong to methylotrophs. Many bacterial methylotrophs are capable of assimilating methane, and these are often called methanotrophs.
Central metabolism of methylotroph is a reaction of converting formaldehyde into an organic matter having a C—C bond after converting methanol to formaldehyde. As shown in FIG. 2, as a carbon assimilation metabolism pathway via formaldehyde, a serine pathway, a ribulose monophosphate pathway (RuMP pathway), and a xylulose monophosphate pathway (XuMP pathway) can be recited. Methylotrophs classified into bacteria (methylotrophic bacteria) have a serine pathway or a RuMP pathway. On the other hand, methylotrophs classified into yeast (methylotrophic yeast) has a XuMP pathway.
Methylotrophic bacteria are classified into obligate methylotrophs and facultative methylotrophs capable of using other carbon compound according to the difference in methanol requirement.